We have two ears, but you might notice that the ears have fairly complicated geometry. Why would that be? Well, it turns out that the various parts of the ear bounce sound, and sound coming from different directions, both azimuth and elevation, bounces differently. Your brain is very good at figuring this out. This wikipedia page on Sound Localization is quite informative.
It turns out that humans have among the best direction-sensing hearing of any animal.
[disclaimer -- I work for Dolby, but in their imaging group]